Evaluation of the biocontrol potential of PGPB strains isolated from drought-tolerant tomatoes against fungal pathogens

Despite being important to maintain the increasing demand of food to the growing population, agrochemicals such as pesticides and fertilizers pose a major threat to both human health and the environment by triggering biodiversity loss. Plant Growth Promoting Bacteria (PGPB) constitute a promising potential alternative for increasing crop yields and alleviating stress in plants. The present study aims to evaluate a broad number of rhizospheric and endophytic PGPB strains isolated from a drought-tolerant tomato landrace, as potential biological agents. A total of 49 strains were tested for their in vitro antifungal capacity against seven fungal pathogens. Antagonistic strains were further screened for various antifungal and PGP traits. Our results revealed that 10 bacterial strains were active against one or more fungal pathogens, while eight and five strains were able to produce ammonia and hydrogen cyanide, respectively. By contrast, only three strains were unable to produce hydrolytic enzymes. The most efficient strain, SAESo-E4 (Azotobacter chroococcum) was further evaluated in planta as biocontrol agent against Sclerotinia sclerotiorum. Lettuce plants inoculated with SAESo-E4 showed resistance to fungal infection as indicated by the lower Disease index, and membrane lipid peroxidation compared to the non-inoculated plants. Moreover, analysis of polar plant metabolites by GC-MS revealed that induction of defence-related and signaling biosynthetic pathways were more pronounced in plants inoculated with the pathogen, while plants treated with SAESo-E4 showed an upward trend in photosynthesis and growth. Collectively, these results demonstrated that SAESo-E4 can probably serve both as an effective biological agent and a biostimulant.

Automated summary

Agrochemicals pose a major threat to human health and the environment, while Plant Growth Promoting Bacteria (PGPB) offer a potential alternative to increase crop yields and alleviate plant stress. This study evaluated rhizospheric and endophytic PGPB strains from a drought-tolerant tomato landrace as potential biocontrol agents. Results showed that 10 bacterial strains exhibited antifungal activity, while 8 strains produced ammonia and 5 strains produced hydrogen cyanide. The most effective strain, SAESo-E4, showed resistance to fungal infection in lettuce plants and induced defense-related and signaling pathways.